This invention relates generally to implantable medical pumps, and more particularly to an implantable medical pump having a non-volatile programmable memory for restoring the device""s hardware and software operating parameters.
Implantable medical pumps can be used to treat any number of physiological, psychological, and emotional conditions. For some medical conditions, implantable medical pumps provide the best, and at times the only, therapy to restore an individual to a more healthful condition and a fuller life.
The medical pump provides the patient with a programmable level of dosage or infusion of a drug or other therapeutic agent. The pump typically includes a drug reservoir, a fill port, a peristaltic pump having a motor and a pumphead to pump out the drug from the reservoir, a catheter port to transport the drug from the reservoir via the pump to a patient""s anatomy, and the electronics to control the motor. The drug reservoir, fill port, peristaltic pump, and catheter port are generally held in a housing, or bulkhead. The bulkhead typically has a series of passages extending from the drug reservoir and through the peristaltic pump that lead to the catheter port, which is typically located on the side of the housing. The peristaltic pumps use rollers which move along a pump tube, thereby moving liquid through the tube. Some form of fluid flow control is also provided to control or regulate the flow of fluid medication from the reservoir to the outlet of the device for delivery of the medication to the desired location in a body, usually through a catheter.
Examples of drug infusion pumps currently available are the SynchroMed(copyright) programmable pump sold by Medtronic, Inc. of Minneapolis, Minn., and those disclosed in U.S. Pat. No. 4,692,147 (Duggan), U.S. Pat. No. 5,840,069 (Robinson), and U.S. Pat. No. 6,036,459 (Robinson).
The drug delivery pump also includes electronics (typically a processor and associated other hardware) to provide a prescribed dosage of drug under a set time schedule. Various treatment parameters such as the dosage, the rate and timing prescribed by the clinician are entered into the pump using an external computer-like device called a physician programmer and stored in a Random Access Memory (RAM). The programmer communicates with the pump by telemetry. This also allows the clinician to determine how the pump is operating at any given time. The clinician can also can use the programmer to change the treatment parameters such as the medication dosage. The various electrical components of the pump such as the processor and the memory devices, except the power source, can be designed using on one or more Application Specific Integrated Circuits (ASICs).
Once the pump is implanted, however, any number of complications may occur. For example, the RAM, which stores the treatment parameters for the drug therapy, may become corrupted. Corruption of the RAM may occur for any number of reasons including for example: (1) a temporary drop in the device""s battery voltage (due to Electro-Magnetic Interference (EMI) or an internal power surge); (2) software execution malfunctions (such a bug or a temporary bit flip within the processor which causes erroneous program execution); or (3) latent RAM cell failures where the RAM cell loses its ability to hold programmed values over time. If the RAM is corrupted, the pump must be reprogrammed. However, until the pump is reprogrammed, the pump cannot operate. This is undesirable since the patient loses the drug treatment therapy during this time and may even go into withdrawal.
Another example of a complication is that it may become necessary to adjust trim parameters stored within the ASIC. Trim parameters are default settings such as voltage references and bias currents stored in the ASIC. Each ASIC will have a unique set of trim parameter values that are calculated by electrically testing the chip and measuring the trim parameter values. Using a laser trimming process, the trim parameter values are permanently stored on the chip. This laser process trims away chip material to change characteristics of the chip including, for example, the resistance value. Again, the trim parameters values in the ASIC are permanently stored values and cannot be adjusted after manufacture. This is problematic since the trim parameters values may need to be subsequently adjusted due to a number of reasons including for example: (1) trim parameters shifting due to age; (2) a dependence to other pump components; (3) additional performance data that is subsequently gathered; or (4) simply due to manufacturing trim errors. Laser trimming is also a time consuming process.
Accordingly, it is desireable for the implantable drug pump to continue providing treatment therapy based on default settings even after detecting corruption of therapy data in memory. It is also desireable to provide an implantable drug pump with programmable trim parameters that may be adjusted after manufacture or after implant.
The present invention uses various types of volatile and non-volatile memory devices within an implanted drug infusion pump to provide a safe and robust programmable system, able to back-up and restore the device""s hardware and software operating parameter values in the event of memory corruption and as an alternative to hardware trim techniques.
In a preferred embodiment, the present invention includes a processor, a Read Only Memory (ROM), a Random Access Memory (RAM), and an electrically erasable programmable read-only memory (EEPROM). The EEPROM provides a programmable non-volatile memory wherein customized operating parameter values of the pump and the trim parameter values of the integrated chip(s) may be stored. The values stored in the EEPROM may then be relied upon during times when the other memory devices become corrupted. These values may also be adjusted to account for changing conditions of the pump and the treatment therapy. Further, the ROM provides a form of non-programmable, non-volatile memory wherein a safe-mode set of parameter values may be stored. In the event that both the RAM and the EEPROM have become partially or fully corrupted, the pump may at least operate in a safe-mode. Advantageously, the present invention provides a multi-layer backup mechanism to ensure continued operation of the implantable drug pump during corruption of the memory. Further, the trim parameter values may be subsequently adjusted without having to explant the pump and replace the integrated chip(s).